Combustion noise eliminator



June 4, 1968 R. T. BRADY ET AL COMBUSTION NOISE ELIMINA'IOR 2 Sheets-Sheet 1 Filed Dec. 14, 1966 NQE INVENTORS ROBERT T. BRADY OZGUN ZARTAL I 5Y1! r- ATTORNEY June 4, 1968 BRADY ET AL COMBUSTION NOISE ELIMINATOR QUE 5m 6 om om 2 Sheets-Sheet 2 Filed Dec. 1.4, 1966 5% 3 (LHEHHONVIA NOLLISNVtLL MDVLS W085 EDNViStG' INVENTORS ROBERT T BRADY OZGUN HKATEAL ATTORNEY United States Patent 3,386,395 COMBUSTION NOISE ELIMINATOR Robert T. Brady, Elmhurst, and Ozgun Kartal, Chicago, Ill., assignors to Vapor Corporation, Chicago, Ill., a corporation of Delaware Filed Dec. 14, 1966, Ser. No. 601,734 6 Claims. (Cl. 110-184) ABSTRACT OF THE DISCLDSURE This invention relates in general to a combustion noise eliminator, and more particularly to a method and apparatus for eliminating combustion noise generated during the operation of a boiler or steam generator, and still more particularly to a simple and inexpensive method and apparatus for conditioning the stack of a boiler to eliminate combustion noise generated thereby.

With the advent of highly eflicient combustion systems for boilers or steam generators, combustion noise generted by such a boiler has created a problem in boiler installations and especially where the noise is objectionable to nearby residents. These highly eflicient combustion systems necessarily require early intimate mixing of the fuel and oxidizer and the forcing under pressure of a fuel-oxidizer mixture into a confined combustion area. Further, the usual compact combustion chamber necessitates a short fuel particle residence time making it man datory that the continual mixing of partially burned fuel and additional oxygen must be maintained. Zones of stable and unstable vortices are generated by such mixing, and depending upon the fuel-air ratio in each vortex, a certain firing frequency and rate is maintained. While the calculated fundamental frequency of most combustion systems ranges between twenty and forty cycles per second, random explosions associated with efficient combustion are heavily populated in this range thereby rendering the system easily excited. It should be appreciated that the calculated natural frequency may be outside of this range. This excitation results in objectionable pulsations, rumble, throbbing and drone. The present invention involves determining the stack anti-node 'or anti-node of a standing wave in a stack of a combustion system and thereafter conditioning the stack to destroy the antinode and thereby eliminate the pulsations, rumble, throbbing and drone.

The openings in the stack may be of any suitable type,

but must have a predetermined area range and be locatedat a predetermined height.

Heretofore, stack noise mufflers have been developed which involve complex baffle arrangements that are costly and cause excessive pressure losses. Further, it has been known to provide quarter wave rectifiers at the pressure anti-node, but such required too much space outside the stack, are costly in materials, and are prone to fail due to corrosion.

Accordingly, it is an object of the present invention to avoid the above named difficulties and provide a method and apparatus for eliminating combustion noise in a combustion system that is inexpensive and does not require any additional space or materials.

Another object of the present invention is in the provision of a new and improved method and apparatus for eliminating combustion noise in a combustion system including a boiler having a stack extending generally upwardly therefrom.

Still another object of the present invention is to provide a combustion noise eliminator for eliminating pulsations, rumble and drone and for reducing throbbing, all of 3,386,395 Patented June 4, 1968 ICC which are normally associated with high efficiency, compact combustors.

Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 is a diagrammatic View of a combustion system including a boiler and a stack and illustrating the application of the present invention for eliminating combustion noise;

FIG. 2 is a view similar to FIG. 1 but showing the combustion system in side elevation;

FIG. 3 is an enlarged sectional view taken substantially along line 33 of FIG. 1;

FIG. 4 is a sectional view of a boiler having a stack thereon and illustrating the standing wave profile in the stack; and

FIG. 5 is a graphical illustration of the application of the present invention to combustion systems having various sizes of stacks.

Referring now to the drawings, and particularly to FIGS. 1-3, a boiler installation is illustrated with the present invention wherein a boiler 10 is shown mounted on a suitable pad '11 within a building 12. A stack transition flange 13 is arranged at the upper part of the boiler and onto which is mounted a stack 14 that extends upwardly therefrom and through an opening 15 in the roof 16 of the building. Any suitable means may be provided at the roof to seal against the outside elements passing between the stack and roof opening.

The method of the present invention includes the steps of determining the stack anti-node or anti-node of a standing wave in the stack, and thereafter providing a suitable opening in the stack at the anti-node. Determination of the stack anti-node may be made by any suitable instrumentation equipment, and an opening in the stack at the anti-node may be made by any suitable method, The length and diameter of the stack is determined by the capacity of the boiler or boilers served by the stack, althrough it can be appreciated that the type and size of stack installation is many times determined by the building within which the boiler is installed.

Further, in some installations, a stack anti-node is formed in a plurality of places along the stack, and then it is only necessary to apply the present invention to one of these places in order to eliminate combustion noise. The opening in the stack 14 is indicated generally by the numeral 17, and it is noted that such is located above the roof. It is at least preferable to locate the opening above the roof. An example of applying the present invention, as seen in FIGS. 1 and 2 where the boiler has a capacity of two hundred boiler horsepower and the stack length is about forty-five and one-half feet above the stack transition flange 13-, involves determination that a stack antinode is located about seven and one-half feet from the upper end thereof, and therefore the opening 17 is located at the anti-node. A proper diameter of such a stack would be about eighteen inches, and it has been found that about nine square inches of opening will serve to solve any combustion noise problem. While the opening 17 may take any suitable form, it is illustrated as twelve equally spaced one inch in diameter holes. It is not necessary that the holes be circular or that they all be at exactly the same height, but it is necessary that about nine square inches of opening be provided even though a smaller or larger opening will also work. The distance above the stack flange height for positioning of the opening 17 is illustrated by the line 18, while the distance above the opening to the upper end of the stack is indicated by the line 19. It should also be appreciated that the holes 20 defining the opening are the easiest and most economical to apply especially to an existing structure.

In FIG. 4, a typical boiler 10 is shown that includes a combustor 21 defining a confined combustion area into which is forced under pressure a fuel-oxidizer mixture which pursuant to combustion delivers hot combustion gases to a coil 22 having water pumped therethrough. The combustion gases after performing work on the coil 22 pass into a collection chamber 23 and ultimately into the stack 14 and upwardly into the atmosphere. A typical representation of a standing sound wave is illustrated at 24 which normally would cause pulsing, rumble, throbbing and drone during operation of the combustion system, and which is intended to destroy by the present invention. The anti-node of the standing wave is illustrated at 25, an it would be at about this location that openings would be provided in the stack to destroy the standing wave and thereby eliminate combustion noise. Depending upon stack height, the anti-node may appear in one or more places along the stack length, and graphical illus tration of anti-node location in stacks of varying height is shown in FIG. 5. While a maximum of two places is shown in FIG. 5, more than two would be present for even higher stacks.

Referring now to FIG. 5, the stack height above the transition flange is plotted along the horizontal, while the distance from the stack transition flange in feet is plotted along the vertical. The positioning of the openings is illustrated for stacks 26 to 35 of varying height. Note that a single choice of opening location is provided for stacks 26 to 30, while a dual choice of location of the opening is provided for stacks 31 to 35 and additional locations would be available for stacks of greater height than shown in FIG. 5. The preferred location of the opening is illustrated by the diamond-shaped symbol indicated by the number of the stack and the suffix a, such as 26a, 27a, etc. Further, the range in which the opening may be positioned is indicated by upper and lower cycle symbols designated by the number of the stack plus the letters b and e, such as 26b, 260, 2712 and 270, etc. The preferred locations of the stacks are interconnected by a line 3-6 through stack 30 and thereafter lines 36a and 36b for indicating the location at any point intermediate the lengths of stacks illustrated. Similarly, the upper maximum location of the opening is indicated by connecting the upper plotted points by line 37 through stack 30 and thereafter by lines 37a and 37b. The lower limits are indicated by the line 38 through stack 30 and thereafter lines 38a and 38b. In order to more fully illustrate the range where the opening or openings may be provided along the stack in connection with the various lengths of stacks illustrated, the upper and lower limits are boundaries for a shaded area extending across the graph. It should be further understood that placement of the openings outside the range may minimize combustion noise but not as satisfactorily.

An example of interpretation of the graph in FIG. for a stack height above the flange of thirty-one feet would be to follow the horizontal distance to the thirtyone foot point and thereafter move upwardly until the lines of the ranges are crossed to determine where the opening may be located. In this regard, it is seen that the most effective location would be at point 39 (seven feet) or 40 (twenty-four feet), although the range for the lower point would be between 41 (four feet) and 42 (ten and one-half feet). Similarly, the range for the upper location 40 would be between the point 43 (eighteen feet) and the point 44 (twenty-nine and one-half feet). Preferably, the location of the opening would be above the roof.

The location of the opening is not affected by the diameter of the stack or the capacity of the boiler serviced by the stack, but is only affected by the height of the stack. Thus, for given stack height the holes would be at the same location regardless of stack diameter and boiler size, although the opening is most effective if it is equal to about nine square inches.

In view of the foregoing, it will be appreciated that the present invention involves a new and improved method and apparatus for eliminating combustion noise in a highly efiicient combustion system by providing an opening the stack of the anti-node of the standing sound wave.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention, but it is understood that this application is to be limited only by the scope of the appended claims.

The invention is hereby claimed as follows:

1. In a combustion system including a boiler having a confined combustion area and a stack extending upwardly therefrom, the method of eliminating combustion noise comprising, the steps of determining the location of a stack anti-node, and conditioning the stack at about the location of a stack anti-node to eliminate the anti-node by providing in the stack at said location opening means of about nine square inches intercomrnunicating the interior of the stack with the atmosphere.

2. The method as defined in claim 1, wherein said stack conditioning includes providing opening means in the form of a plurality of holes.

3. The method as defined in claim 1, wherein said stack conditioning includes providing opening means in the form of twelve one inch in diameter circumferentially arranged and equally spaced holes.

4. In a combustion system including a boiler having a confined combustion area and a stack extending upwardly therefrom, wherein the improvement comprises means for eliminating combustion noise including opening means in the staclcof about nine square inches intercommunicating the interior of the stack with the atmosphere along the stack at about the location of a stack anti-node.

5. The improvement as defined in claim 4, wherein said opening means includes a plurality of holes.

6. The improvement as defined in claim 4, wherein said opening means includes twelve one inch diameter circumferentially arranged and equally spaced holes.

References Qited UNITED STATES PATENTS 2,297,046 9/ 1942 Bourne 18148 3,265,040 8/1966 Chen 122--4 FOREIGN PATENTS 589,090 6/1947 Great Britain.

JAMES W. WESTHAVER, Primary Examiner. 

